Cellulose-nitrate plastic



Patented Apr. 23, 1929.

UNITED STATES PATENT OFFICE.-

GEORGE L. SCHWARTZ, OF WILMINGTON, DELAWARE, ASSIGNOR TO E. I. DU FONT DE NEMOURS & COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION OF DELA- WARE.

CELLULOSE-NITRATE PLASTIC.

N Drawing.

This invention pertains to cellulose nitrate compositions containing a composite softener, and relates particularly to the manufacture of artificial leather of which films or layers of pyroxylin constitute an essential art.

One object of my invention is to improve on modifiers or softeners for films or other cellulose nitrate plastics.

Another object of my invention is to provide cellulose nitrate compositions which can be used as a coating on woven fabrics to produce artificial leather or fabrikoid having great durability and pliability.

By the term softener I mean a material of such low volatility that said material will remain for a long period as a constitutent of the pyroxylin coating or-film of which it originally formed a part. I have found it convenient to divide the softeners for cellu-' lose nitrate into two main classes, viz, solvent softeners and non-solvent softeners.

The solvent softeners, as their name implies, have a substantial solvent action on cellulose nitrate, whereas the nonsolvent sof teners are practically devoid of any such action. This. solvent action of the solvent softeners is an action which is effective at ordinary temperatures, that is, temperatures between 10 and 0., with the result that the pliability of a cellulose nitrate film contain ing said softener is substantially increased at ordinary atmospheric temperatures. These solvent softeners, which form one element'of 35 my invention, may be described as active solvents to distinguish them from the so-called latent solvents.

The softener commonly used at the present time in artificial leather is castor oil, a nonsolvent for cellulose nitrate. Various other vegetable oils, all non-solvent softeners, have also been suggested for this purpose. Solvent softeners in general ten-d to impart greater flexibility to pyroxylin films than do non-solvent softeners, but the difliculty encountered in using them is that they render the film so sticky that it cannot be satisfactorily embossed. 7

I have now discovered that the objectionable stickiness caused by the solvent softener may be overcome, and at the same time a substantial increase in pliability obtained, by using the solvent softener in combination with a non-solvent softener.

Application filed June 16, 1921,

For the non-solvent softener, I have found it advantageous to use a member of a class of substances which may be generically designated esters of higher aliphatic acids. As

examples of this class of substances there may be cited certain vegetable oils such as castor oil,- blowncottonseed oil, and preferably the oils with a low iodine number such as blown or unblown cocoanut oil, all of these oils being composed chiefly of glyceryl esters of higher aliphatic acids; and there may also be cited the synthetic esters such as ethyl palmitate, the glycol esters of the fatty acids .the relatively non-volatile aromatic esters, as

for example, (1) triphenyl phosphate ortho-, meta-, or para-tricresyl phoshate, and orthometaor para-cresyl esters of cocoanut oil acids, and (2) esters of aromatic acids such as neutral phthalic acid esters of alcohols having from 2 to 6 carbon atoms, benzyl benzoate and amyl cinnamate. Suitable phthalic esters are ethyl butyl phthalate, dibutyl phthalate and diamyl phthalate. As an instance of a solvent softener other than an aromatic ester there may be cited xylene-sub phon-methylamid. 1 a

The ratio of solvent softener to non-solvent softener used in practising my invention may vary within wide limits, depending not only upon the conditions to which the film or artificial leather is to be subjected, but also upon the particular substances employed as softeners. In any case, sufficient non-solvent softener is incorporated in the composition to mask or overcome the stickiness caused by the solvent softener.

The ratio of pyroxylin to total softener will ordinarily be between 1 to 0.75 and 1 to 2.0.

A solvent softener which I have found to be especially valuable as an element of a composite softener is di-(normal) butyl phthalate. This substance may be produced in the following way:

Three parts by weight of phthalic anhydride are added to 3 parts of normal butyl alcohol (B. P. 115-117. C.) and the mixture heated to 117 C. for eight hours. This completes the first reaction with the formation of mono-butyl phthalate which remains dissolved in the excess alcohol. Three percent by weight ofdry hydrogen chloride is dissolved in the mixture, which is heated to 117 for eight hours. The second reaction is accompanied by the separation of a layer of water. This is separated and the heating continued for an additional eight hours. The resulting liquid product is first washed with water to remove the hydrochloric acid; then with strong sodium carbonate to remove the monobutyl phthalate and any free .phthalic acid; and finally with water several times until neutral. The di-butyl hthalate is purified from alcohol and dried y passing a current of air through the liquid heated to 160 C. The product is a liquid, odorless, slightly yellow in color and may be obtained water white by distilling under diminished pressure. The yield is 83.6% of the theoretical. Boiling point under 29 mm. pressure is 210 C.

A few of the specific softener compositions which may be used in accordance with my invention may be tabulated follows:

I. Castor oil 100 parts Di(normal) butyl phthalate 5 to 10parts Pyroxylin parts II. Blown cottonseed oil 100 parts Dibutyl phthalate 6 parts Pyroxylin -4 53 parts III. IV. V. Dibutyl phthalate: 80. 60 45 parts Ethyl palmjtate 25 parts Liquid petrolatum; 20 15 15 parts Cocoanut oil 40 parts Pyroxylln 100 -100 100 parts VI. Tricresyl phosphate Q parts Ethyl palmitate 15 parts Liquid petrolatum 10 parts Pyroxy 100 parts Excellent results may be obtained with a mixture containing 40 to 50 parts of dibutyl phthalate and from about 60 to 50 parts of cocoanut oil plus liquid petrolatum, for each 100 parts of pyroxylin. As will be evident from the above exam ples, the smaller the ratio of solvent, to nonsolvent, softener, the greater is the ratio of total ,softener to pyroxylin./

As will be understood bythose' skilled in the art of making artificial leather, the mixtures covered by the above examples are dissolved in a suitable solvent, such as a mixture ofequal parts of ethyl acetate and benzone, and theresulting solution is then applied to a fabric and the solvent'allowed to I evaporate.

As has been indicated above, the chief function of the non-solvent softener, when a relatively large amount of solvent softener is used,

' iszto act as a lubricant to preveht the surface film of pyroxylin from sticking to the embossing roll during the embossing operation.

In order to obtain the maximum pliability through the use of a solvent softener, I pr ferably use the solvent softener alone in the base coats of the artificialleather goods a d the combination of solvent and non-solvent softener in the upper (i. e. exterior) coat or coats only. The non-solvent softener in the exterior coat will prevent adhesion of the pyroxylin surface to the embossing roll, while the large proportion of solvent softener in the base coats will render the coated fabric exceedingly pliable.

Another advantage of a mixture of a solvent softener with a non-solvent softener is that the tendency toward exudation displayed by a non-solvent softener is very much reduced by the presence of the solvent softener. A solvent softener is practically non-exuding, so that the ratio of non-solvent softener to solvent softener will be determined in some cases by the requirements to be met in regard to avoiding exudation,

A pyroxylin'coated fabric suitable for embossing may be prepared, for example, by applying two base coats in which the softener is composed of dibutyl phthalate, the ratio of pyroxylin to softener being 10 to 8 and then applying two additional coats having a composition such as that set forth in any one of the above examples numbered I to VI.

It will be noted that in Examples III to VI, the liquid petrolatum is used in conjunction with another non-solvent softener; the main reason for this is as follows: In attempting to use liquid petrolatum'alone as a lubricant it was soon found that enough of this lubricant could not be added to give the necessary absence of stickiness without causing precipitation of the pyroxylin. I then discovered that this difficulty could be overcome by adding a non-volatile neutral ester of phthalic acid,

and a non-solvent softener.

'2. A product comprising cellulose nitrate, a non-volatile neutral butyl ester of .phthalic acid, and a non-solvent softener.

3. A product comprising cellulose nitrate, dibutyl phthalate, and a non-solvent softener.

4. A product comprising cellulose nitrate,

di-(normal) butyl phthalate, and a non-solvent softener. v

5. A product comprising cellulosenitrate, a non-volatile neutral ester of phthalic acid, and a non-solvent softener comprising an ester of a higher aliphatic acid.

6. A product comprising cellulose nitrate, from about 5 to 10 parts of a non-volatile neutral butyl ester of hthalic acid, and about and a non-solvent softener comprising an 100 parts of a non-so vent softener comprisester of a higher ali hatic acid and a noning an ester of a higher aliphatic acid. volatile oily paraflin ydrocarbon.

7. A product comprising cellulose nitrate, 9. A product comprising cellulose nitrate,

6 a solvent softener, and a non-solvent softener from 40 to 50 parts of dibutyl phthalate, and 10 comprising an ester of a higher aliphatic acid from 6" to 50 parts of a non-solvent softener and a non-volatile oily saturated hydrocarcomprisin an ester ofahigher aliphatic acid bon. plus liqui petrolatum.

8. A product comprising cellulose nitrate, In testimony whereof I afiix my si ature. 10 a non-volatile neutral ester of phthalic acid, GEORGE L. SCHWA TZ. 

